This invention relates to vehicle suspensions and especially, but not exclusively, to suspensions for heavy load-carrying vehicles, such as, trucks and other similar types of commercial vehicle.
In a known type of vehicle suspension, such as that disclosed and claimed in our co-pending International Patent Application No. PCT/GB90/00436 (Publication No. WO 90/1121) entitled "Vehicle Suspension System", stabilizing means in the form of an anti-roll device, such as, an anti-roll tube or bar, is fastened transversely of a vehicle between the springs on opposed sides thereof, to provide the vehicle with an anti-roll characteristic.
Such a transversely arranged anti-roll device neither bears nor creates any force when the vehicle suspension is undergoing so-called "straight axle, static bounce" motion, because the respective springs on opposed sides of the vehicle deflect by substantially the same amount and in the same direction. In this manner, the components by which the anti-roll device is attached to the associated springs and the device itself are rotatably deflected by substantially the same amount.
During rolling motion of the vehicle, however, the springs on each side of the vehicle deflect in different directions, such that the components by which the anti-roll device is attached to the springs, attempt to rotate in different directions, thereby twisting along the length of the transverse anti-roll device. Resistance to this torsional strain creates, in turn, a moment in the springs thereby stiffening-up their opposing movements during vehicle roll. Thus, the springs are effectively stiffer during vehicle rolling motion than in straight axle, static bounce motion, due to this anti-roll effect.
Such anti-roll means may also carry secondary suspension means in series or parallel with the suspension springs which effectively constitute primary suspension means, with the secondary suspension means softening the total rate of the overall suspension. Such secondary suspension means may be in any suitable form, such as, leaf springs or air or elastomeric cushions, and can be positioned at various locations transversely of the vehicle. Such locations for the secondary suspension means may be in-line with the springs of the primary suspension means or outboard or inboard thereof. The inboard secondary suspension means may also be combined into a single unit, such as, a spring.
Accordingly, it is an object of the presently inventive suspension to improve the operating characteristics of known suspensions of not only the type described above but also any other suspension system including other forms of transverse anti-roll means subject to rotation during straight axle, static bounce motion of the vehicle.
Another object of the present invention is to increase the spring rate of a suspension proportional to increased suspension spring deflection during straight axle, static bounce motion, thereby enabling the vehicle to carry heavier loads than previously.
A further object of the invention is to reduce peak stresses in the leaves of a suspension spring, thus enabling the spring to carry a higher load without being overstressed.
Yet a further object of the invention is to utilise the anti-roll device to achieve one or more of the above-mentioned objects of the inventive suspension.